Let me ask you this. Why do you want a canopy? Unless the tank has to go in a more or less formal room like a living room, a canopy really gets in the way of working on the tank, and if you have lighting mounted in it, makes it even harder to deal with. I'd say either shipe the canopy entirely or make it strictly decorative, mounting the lighting by other means.
Note that many LED fixtures mount from cables or to brackets tat attatch to the tank or stand.
As for exactly how many fixtures you'll need that depends a lot upon the lighting effects you want in the tank. For a rough estimate you can figure each LED fixture will cover about a 2 foot length of tank, but this can vary depending upon the fixture, it's lens system and what your trying to do with the lighting.